Offices represent one of the largest commercial space uses in the country, making them a focus of energy conservation efforts. The prototypical office lighting modules in the Advanced Lighting Guidelines are designed to consume 25% to 30% less energy than ASHRAE/IESNA Standard 90.1-2007. However, energy conservation is not the whole story. Lighting for offices today must be “energy effective”, that is, use energy wisely to create a work environment that is both productive and comfortable. Given the prevalent use of computers in the modern workplace, the qualitative aspects of lighting are now more important than ever. These modules aim to maintain acceptable lighting quality by controlling glare, distributing light on the vertical surfaces, and by providing luminous balance, uniformity and natural color.

Studies have shown that lighting not only has a significant impact on the ability of office workers to perform short term visual tasks, but can also increase long term performance and overall worker satisfaction. The importance of quality in office lighting cannot be overstated. Unlike retail or public spaces where occupants move about for short durations, office workers customarily spend a full day at the same desk in the same work environment. When the majority of waking hours are spent in the office, the visual environment and lighting quality become paramount. Employees’ salaries are typically the costliest part of running an office, so, for example, if poor quality lighting distracts a worker only 1% of the time, this could equate to a $5 per square foot annual loss in productivity. Quality office lighting has other long-term benefits like increased employee retention and reduction in absenteeism.

The qualitative issues that are deemed “very important” for office lighting by the IESNA Design Guide* are:

daylighting integration

glare

luminances of rooms surfaces

appearance of space and luminaires

geometrical relationship between the light source, visual task and viewer.

Attributes listed as “important” by the IESNA include:

good color

distribution

facial modeling

lack of harsh shadows.

These qualitative issues are discussed in more detail below:

*IESNA Lighting Handbook 9th Edition Design Guide Chapter 10

Daylighting Integration: Daylight (light from the sky) should be the primary source of general lighting in an office to the greatest extent feasible. Daylighting can provide a continuous spectrum of visible light and the high levels of illumination beneficial for maintaining healthy cycles of wake and sleep Windows can provide a desirable connection to the outdoors. Workers near the windows have the added benefit of distant views that allow their eyes to change focus and relax from close-up office work. At the same time, workers should be protected from the glare and thermal discomfort of direct solar penetration without proper sun control. While sun patterns can be desirable in break areas and circulation paths, they should be avoided within the direct field of view of a worker, in order to prevent harsh contrasts that may be visually debilitating. The direct rays of the sun are best controlled on the exterior of a building before the sunlight and heat enters the interior, but they can be controlled on the interior with blinds, shades, or interior light shelves.

Direct and Reflected Glare control: Both direct and reflected glare can be distracting to workers and increase the difficulty of performing visual tasks, potentially resulting in a long-term loss of productivity. Office workers at fixed desk locations are particularly vulnerable to glare problems, because they cannot easily change their physical relationship to the source, be it a luminaire or a window.

Luminances of Room Surfaces: Lighting the walls and ceilings can be just as important as lighting the task. Proper lighting of the space contributes to the adaptation level of the eye, mitigates glare and reduces shadows – all of which improves visual performance. In addition, well-lighted room surfaces provide a more pleasant, brighter-looking workspace; which can be easily dismissed if not for the contribution to mental stimulation, long term work performance and employee satisfaction.

Appearance of Space and Luminaires: The visual hierarchy of surface brightness and the layout and style of luminaires can strongly influence the character of an office. A balance should be achieved between the desire for visual interest of the luminous environment and the need for visual comfort. Lighting should be designed to aid in orientation of the space and avoid visual clutter.

Light Distribution: A relatively uniform distribution of light, without strong shadows, is preferred for office environments. Luminance ratios should be fairly uniform. A 3:1 (maximum to minimum) is preferred between the task illuminance and the immediate surround. Outside of task areas, a wider range of luminance ratios are acceptable: up to 10:1 for surfaces in the field of view, and up to 20:1 for the contrast between window or luminaires and the task surface. At the other extreme, a totally uniform distribution of 1:1 will be shadowless and make people, objects and interiors appear flat and dull. The use of computers has transformed the luminous work environment. Initially, computer screens were darker than paper-based tasks and prone to veiling reflections. Now screen luminances can fluctuate between very dark (CAD at 3 cd/m2) to very bright white (200-450 cd/m2). The same worker may be operating at both extremes in short succession. The size of the screen within the field of view will determine the impact of the screen luminance on the workers adaptation level, and the importance of other luminances in the field of view. Providing the worker with adjustment options for the location of their monitors and the brightness of their screens will allow them to modify their environment for their own comfort.

Reflectances and Finishes: To achieve the desired uniformity and luminance ratios, wall and ceiling surfaces, as well as modular office partitions, furniture, overhead bins and fabrics should have high reflectances, i.e., be light in color. Finishes should be matte or eggshell. Office ceilings should be a minimum of 80% reflectance, with 90% preferred. Walls and furniture should be 65-70% reflectance and floors not less than 20% reflectance. Polished, glossy and shiny surfaces should be avoided in office work areas because they can be a source of reflected glare. In addition to providing uniformity, high surface reflectances can reduce the amount of light that is needed, thereby reducing energy consumption. Energy effective offices need not be colorless. Low reflectances, i.e., darker and saturated colors, may be used for surfaces and furniture below the level of the worksurfaces, for accent and interest.

Shadows: In a work environment, shadows under overhead cabinets or shelves can create a distracting and excessive luminance contrast and make a work cubicle feel gloomy. This can be mitigated through the use of low-output undershelf luminaires. Luminaires mounted in the ceiling with a totally direct distribution, like those from recessed parabolic troffers, can be another source of harsh shadows. These direct luminaires generally will not result in comfortable luminance ratios without the addition of an indirect component. Thus a combination of direct and indirect lighting distribution is preferred for office applications.

Relationship between Light Sources, Visual Task and the Viewer: It is the geometry between the light source, task, and viewer that determines the presence of direct or reflected glare. Luminaires with strongly directional distributions are not the appropriate choice as the standard fixture in a flexible open office space, as the geometrical relationships between light source, task, and viewer cannot be fixed and direct and overhead glare cannot be avoided. Undercabinet lights should not be located directly in front of the viewer because the angle of light creates veiling reflections, although this can be partially mitigated by the use of special linear lenses. Computer screens should be located (or be adjustable) to avoid reflections from windows and luminaires.

Facial Modeling: A large proportion of communication in offices is non-verbal, relying on facial expressions and body language. Illumination that is only directed downward can cause unflattering, unnatural and even confusing shadows as well as distort three-dimensional perception. Some portion of indirect lighting or interreflections (light reflected from the walls and ceilings) is needed to allow faces and objects to appear more natural. Appropriate facial modeling is especially important in meeting rooms and video-conference rooms.

Energy Effective Office Layouts:

Energy efficiency is not a function of lighting decisions alone. The greatest energy savings from lighting and daylighting occur through careful integration of the lighting with the architecture, building envelope, and HVAC. However, many office lighting projects are associated with rental spaces and tenant fit-outs. Even in these circumstances, when the design team cannot make changes to the envelope or mechanical systems, much greater savings are achievable by an integrated approach to the layout of offices. These include:

Locate the open-plan offices adjacent to the window wall: This layout strategy, coupled with low-height or translucent partitions, high ceilings, and light colored finishes, creates the best opportunities for energy savings. This is because daylight harvesting is more cost effective when occupancy is relatively continuous.

Increase the density and occupancy of workstations while lowering partition heights: Consider temporary “hotel–style” work stations in lieu of permanently assigned but rarely occupied workstations. Create common “quiet rooms” to provide occasional acoustical privacy in lieu of specifying tall partitions for each cubicle. Both daylight and electric light are more efficient with lower partitions, and views to the windows are greatly improved.

Increase the proportion of open-plan offices to enclosed offices: Enclosed private offices tend to utilize light less efficiently than open office plans because of their lower density occupancy. Full-height walls also absorb more of the initial illumination, further decreasing the overall system efficiency.

Locate the private offices away from the perimeter: Because these spaces are less frequently occupied, vacancy sensors typically save most of the energy, reducing the cost-effectiveness of daylight harvesting. The use of glass partitions (with some visual privacy) separating the private offices from the open-plan can give occupants a connection to the perimeter and some spill lighting from the ambient office lighting. Lower ceilings in interior private offices can accommodate most of the HVAC equipment, allowing higher ceilings in the open-plan spaces near the window.

The lighting design strategies and technologies herein can provide office occupants with a safe, comfortable and cost-effective lighting system, while reducing the owners’ energy and maintenance costs. The Advanced Lighting Guidelines offer recommendations for the following specific space types commonly found in offices: